Fare-quasiquote — Quasiquote Patterns for Trivia

fare-quasiquote is a Common Lisp library by François-René Rideau that extends the standard quasiquote syntax to act as a structural pattern in trivia (and other pattern-matching libraries). It enables patterns of the form `(operator ,var1 ,var2) to match list structure and bind sub-expressions.

Online documentation:

• github.com/fare/fare-quasiquote
• trivia wiki: fare-quasiquote integration

Without fare-quasiquote, trivia cannot use quasiquote patterns. With it, the (in-readtable :fare-quasiquote) declaration enables the extended reader, and the patterns `(+ ,l ,r) become valid:

(named-readtables:in-readtable :fare-quasiquote)

(ematch sexp
  (`(+ ,l ,r) (make-instance 'plus :l (parse l) :r (parse r)))
  (`(* ,l ,r) (make-instance 'mult :l (parse l) :r (parse r))))

The pattern `(+ ,l ,r) matches a three-element proper list whose:

• first element is the symbol +
• second element is bound to l
• third element is bound to r

Nested patterns work: `(+ (* ,a ,b) ,c) matches (+ (* 1 2) 3) and binds a, b, c.

fare-quasiquote works through named-readtables: the package header declares the readtable, and every file that uses quasiquote patterns needs:

(named-readtables:in-readtable :fare-quasiquote)

tolk.asd lists :trivia.quasiquote as a dependency, which loads fare-quasiquote automatically.

• Trivia — the pattern-matching library that fare-quasiquote extends
• Named-readtables — the readtable mechanism that activates fare-quasiquote
• Tolk — uses fare-quasiquote for parsing